there are a ton of intro sites to php, essentially php is a server based program, meaning, everything is generated server side, then presented to the viewer through html. if i really wanted to explain it, it would be a book or a good sized manual, so i suggest to get your feet wet, for a free resource:
webmonkey!
http://hotwired.lycos.com/webmonkey/01/48/index2a.html?tw=programming
and if u want more tuts goto google and search for php tutorial! good luck, and if you ever get stuck on something, ask away! don't give up 🙂
